Among the existing oil fields in China, oil wells of medium to high paraffin-content, for which the paraffin content in crude oil reaches 10%-40%, account for 80% or greater, in which the paraffin content is high, the crude oil has high viscosity and poor fluidity, and is very easy to coagulate and accumulate, thereby causing paraffin precipitation, scaling and blocking of the upper and lower portions of the oil screen and the oil well pump, increasing the useless power consumption of the oil well pump, reducing the oil pump capacity, and even completely blocking the wellbore to cause production stop.
In order to solve the worldwide problem of oil field production that paraffin in the crude oil crystallizes to block the well, paraffin-control viscosity reduction products have been developed in recent years. At present, the technologies adopted by this kind of products all belong to the technology scope of jet ultrasonic theory. Structures of the earlier products consist of a jet flow generator, an ultrasonic oscillator, a cavitation cavity, a vortex director and a vortex ejector, which can be regarded as the first-generation jet ultrasonic paraffin-control viscosity reduction products. The problems thereof are: the structures of the products are unreasonable and unscientific, and the sound field intensity of ultrasonic wave is weak, resulting in very limited paraffin control and viscosity reducing effects. To this end, the inventors filed an application “Environment-friendly Paraffin-Control Scale-Preventing Ultra-strong Viscosity Reduction Device” for a patent of an invention on Jun. 22, 2007, which has already been granted a patent right with the patent No. ZL200710052537.2. The invention greatly improves the effects of controlling paraffin, reducing viscosity and preventing scaling, and the products thereof can be regarded as the second-generation jet ultrasonic paraffin-control viscosity reduction products. However, the products still have four main problems when used in deep wells, high-paraffin-content wells and heavy oil wells (greater than 1,000 mPa·S): first, as the products performs ultrasonic treatment on pumped (extracted) crude oil mainly by ultra-strong sound waves, when the daily output of the crude oil is large, the intensity of the sound waves is relatively insufficient; second, for high-paraffin-content wells with low water content, certain paraffin control effect can be achieved, but the paraffin control effect is insufficient; third, when the oil well has a large depth, the longer the distance for the treatment of the crude oil by ultrasonic waves is, the weaker the sound field intensity is; and fourth, for the oil wells with relatively large viscosity, generally, only the method of thermal recovery (thermal production) or injection production (i.e., a periodic gas injection or cyclical gas injection method, which comprises injecting a certain amount of wet saturated steam, which is under a high temperature and a high pressure, into an oil layer to heat the crude oil in the oil layer, and then opening the well for recovery. For the thermal recovery of heavy oil by periodic gas injection, a conventional oil pump with a double-hollow sucker rod having an electric heating device is used; and for the thermal recovery of heavy oil by cyclical gas injection, in addition to a double-hollow sucker rod having an electric heating device, the oil pumping system is further provided with a mechanism capable of directly injecting gas from the ground wellhead to the heavy oil layer after shutdown of the machine and stopping of mining, which mechanism injects gas after stopping of extraction (pumping) and extracts (pumps) oil after startup of the machine, and is referred to as an injection-extraction integrated thermal-recovery heavy oil pumping machine. The electric heating device of the double-hollow sucker rod is an auxiliary heating device for heating the crude oil when the viscosity is greatly increased due to continuous decrease of the temperature during the rising process of the crude oil.) can be used, the first-generation products and the second-generation products cannot achieve expected effects, because at the time of thermal recovery or injection production, the oil pumping and the injection of hot gas flow are carried out alternately. First, a hot gas flow is injected to downhole to heat the heavy oil to reduce the viscosity thereof, and then oil pumping is carried out. In the use of the products, the jet opening of the jet nozzle is small and the amount of the heating gas is limited, which greatly affects the viscosity reduction effect, thereby limiting the use of the products.